Method of nitrification



Patented June 2, 1931 UNITED STATES "PATENTI'OFFICE- A AUGUSTUS B.KI'NZEL, OF IBEECHHURST, NEW YORK, ASSIGNOB TO ELECTRO METAL- LURGICALCOMPANY A CORPORATION OF WEST VIRGINIA 7 METHOD or mrarrrcn'rron NoDrawing. Application filed May 11,

This invention relates to the production of thin layers of hard,wear-resistant, nitrogencontaining material on ferrous articles.

The production of a hard, adherent, wear resistant skin or case ofnitrogen-containing material on the surface of ferrous articles whichcontain certain alloy constituents by heating the articles in thepresence of-am; monia at comparatively low temperatures is known. Forexample, the case is commonly produced on aluminum-containing ferrousalloys which contain critical amounts of alumi- 1111111 but the presenceof other alloy constituents in critical amounts will producenitrogen-containing wear-resistant cases on ferrous materials. Toproduce the case, the alloys may be heated in atmospheres of dry gaseousnitrogenous substances, such as ammonia, which give up nitrogen to thealloys. The temperatures generally used are about 450 C. to about 5800., but other temperatures may be used. For the best results thisprocess requires a treatment of fifteen to ninety hours at thesetemperatures in an atmosphere of ammonia to produce a wearresistantnitrogen-containing skin of the re-f quired thiclmess. The time consumedin such a treatment necessitates a large amount of apparatus per unit ofproduct and. makes the process of nitrification costly. Where largearticles are treated or a number of articles areltreated together in thesame container, :1 lack of uniformity of nitrification is a commonoccurrence. More rapid methods of pro,- ducing the wear-resistantcoatings and methods of producing more uniform coatings are desire i Ithas been found that by covering or embedding the alloy article withnon-metallic inert porous material and then heating in the abovedescribed atmospheres, the lack of uniformity described above is avoidedand the rate of nitrification is greatly accelerated. The inertmaterials used are those which are infusible or do not decompose atthetreating temperatures and which have no material effect on the alloys orferrous materials when they are heated to the treatingtemperatures andammonia is not present. The state of 1929. Serial No. 362,447.

rate of nitrification but comparatively coarse aggregates as well asextremely fine powders maybe used. The presence of the inert-materialincreases the rate of penetration of the nitrogen-containing case aswell as the rate of formationof the nitrogen-containing case, but theexact nature of the action of the inert material is unknown to me.

Inert material in the form of powder which is fine enough to conform tothe irregularities of the article is preferred. The inert material maybe calcined, if desired, to remove the last traces of water, but this isnot necessary where harmful amounts of water are not present. Experiencehas shown that powdered carhongnagnesia, silica or asbestos giveexceptionally good results, but other inert ,,materials, such as otheralkaline earth oxides may be used.

hours. Upon cooling, the article was. found to have a uniform, thin,adherent, wear-re sisting, nitrogen-containing coating having a had'ness greater than that corresponding to 1000 Brinell.

An allo article like the article'described in Example was heated to'thesame temperature in the presence of ammonia for four hours but withoutthe'inert material. Substantially no hardening of the surface bynitrification was produced.

II. Articles were embedded in magnesia at the center and at the eightcorners of a container and treated with ammonia as described in ExampleI. The differences in hardness of the surface layers of the articleswere less thrltln the hardness corresponding to 10 Brine Articles of thesame composition were similarly placed -in the same container andtreated with ammonia for a time sufficient to produce a hard nitrogenouscoating but without the inert material. The differences in hardness ofthe surface layers of the article were that corresponding to 300Brinell.

My invention is not limited to the treatment of aluminum-containingsteels. It has been found that the presence of the inert materialaccelerates the formation of the nitro-' gen-containing coatings onother steels amenable to case-hardening by nitrification.

Longer treatments produce thicker layers of nitrified material on thealloys. Thicker layers of nitrogen-containing material are produced withthe same conditions of temperatures and time when the inert material vispresent than when only ammonia is used.

- give up nitrogen to the article, and heating.

3. The method of producing nitrogen-containing coatings on an'alloyarticle which comprises-embedding the article in a closed container 1npowdered magnesia, passing into the container a gaseous substance whichWlll.

presence of ammonia at temperatures below about 580 (3., which comprisescovering the surface to be hardened with porous inert non-metallicmaterial and heating the arti- "cle at said temperatures for about fourhours in the presence of a gaseous substance which will give up nitrogento the article.

8. The method of producing wear-resistant nitrogen-containing coatingson ferrous articles containing a critical amount of alloy substancewhich will produce an adherent nitrogen-containing coating by heating inthe presence of ammonia at temperatures below about 580 (1., whichcomprises covering the surface to be hardened with porous inertnon-metallic material and heating the article at said temperatures forabout four hours in the presence. of ammonia.

9. The method of producing Wear-resistant nitrogen-containing coatingson ferrous alloy articles containing a critical amount of alloysubstance which will produce an adherent nitrogen-containing coating byheating in the presence of ammonia at temperatures below about 580 (3.,which comprises covering the surface to behardened with powderedmagnesia, andheating at said temperatures for about four hours in thepresence of ammonla.

In testimony whereof, I affix my signature.

AUGUSTUS B. KINZEL.

give up nitrogen to the article, and heating iron which comprisesheating the article in contact witha powder of inert non-metallicmaterial and a gaseous substance which will give up nitrogen to thearticle.

5. The method of producing nitrogen-containing coatings on an alloyarticle containing iron which comprises heating the article in contactwith a powder of inert non-metallic material and ammonia.

6. The method of producing nitrogen-containing coatings on an alloyarticle contain ing iron which comprises heating the article to temratures of about 450 C. toabout 580 in contact with a powder of inertnon-metallic material and a gaseous substance which will give upnitrogen to the artig a 4. The method of PIOdllClIlgIlltIOgGIl-COII-taining coatings on an alloy' article contain-

